1. Field of the Invention
The present invention relates to a semiconductor device having a capacitor.
2. Description of the Related Art
In recent years, many efforts have been made to develop ferroelectric memories using a ferroelectric film as a dielectric film of a capacitor, that is, FeRAMs (Ferroelectric Random Access Memories).
A typical ferroelectric film used for a ferroelectric memory is a Pb(ZrxTi1-x)O3 film (PZT film) or an SrBi2Ta2O9 film (SBT film). The PZT is a perovskite compound, and the SBT is a Bi aurivillius phase compound having a quasi-perovskite structure.
If for example, a PZT film is used as a ferroelectric film, electrodes are composed of conductive perovskite type metal oxide films such as SrRuO3 films (SRO films) or the like in order to, for example, improve their fatigue characteristic. For example, Jpn. Pat. Appln. KOKAI Publication No. 2000-208725 and Jpn. Pat. Appln. KOKAI Publication No. 2000-260954 describe ferroelectric capacitors having electrodes each made of a stacked film composed of an SRO film and a Pt film.
Further, what is called a COP (Capacitor On Plug) structure has been proposed in which a capacitor is formed on a plug in order to increase the degree of integration of the ferroelectric memory. In the COP structure, to prevent the plug from being oxidized by thermal treatment, a bottom electrode of the capacitor is partly composed of an Ir film or Ir oxide film, which has an excellent oxygen barrier characteristic.
However, with this structure, Ir disadvantageously diffuses through the conductive perovskite type metal oxide film or a capacitor dielectric film, which degrades the characteristics or reliability of the capacitor. For example, Ir may react with Pb in the PZT film to form a conductive oxide, which increases a leak current of the capacitor or Ir may react with Sr in the SRO film to degrade the crystallinity of the SRO film, which degrades the characteristics or reliability of a dielectric film on the SRO film.
Thus, a problem with the conventional capacitor is that the diffusion of Ir may degrade the characteristics or reliability of the capacitor.